Bumpers are mounted at the forward and rearward extremities of a vehicle to protect the chassis of the vehicle from minor impacts. The bumper is mounted to the lower frame rails of the vehicle chassis for support thereof and functions to withstand minor impacts by collapsing to absorb the energy encountered through the impact.
For conventional bumpers, enhancements to the cross-sectional configuration in the form of reinforcement inserts provide higher energy absorption qualities for those reinforced areas of the bumper, thus achieving some relative improvement in the collapsing of the bumper structure. Such reinforcements are conventionally placed at the attachment points between the bumper structure and the lower frame rails to allow for a greater absorption and dispersion of impact energy by the bumper before this energy is transferred to the lower frame rail into the vehicle chassis.
A more recent development which has been provided to both reduce weight and cost without compromising crash performance has been the introduction of the extruded aluminum bumper. However, known extruded bumpers generate peak and average crash loads having differences so great that the engineer is prevented from designing an optimum bumper system with a crash energy management level of the same order as that of the longitudinal rail member supporting the bumper. If the average crash load carrying capacity of the bumper beam could be increased to the level of the supporting longitudinal member, the bumper peak crash load would cause the supporting rail to collapse prior to triggering the bumper beam crash. This is an undesirable crash mode because of the non-sequential collapse of the front end structural systems.
Accordingly, it is desirable to provide a lightweight bumper configuration that would be capable of crash performance characteristics of heavier conventional bumpers that are formed with reinforcement inserts while allowing the bumper to achieve an optimum crash energy level with a crash load equal to that of the supporting longitudinal rails and without the risk of non-sequential collapse. In addition, reducing the weight of the structure without sacrificing performance of the bumper can provide manufacturing cost savings.